Unit 7 - Lesson 1 - Process Control Flashcards
Challenge with product consistency
Variability in raw materials
What is a process?
A process is a set of actions that transform an input into an output.
Variation vs Variability
Variability is the tendency of something to change or a lack of a regular pattern.
Variation is a change or difference in the properties of something.
Components for consistent process
- Target - value of the process parameter (e.g. temperature) or product parameter (e.g. % abv) that we want to achieve
- Range - a range is thus agreed that represents what is acceptable in terms of delivering customer satisfaction
USL & LSL
The Range Specs
Upper specification limit (USL) or
Lower specification limit (LSL).
Why is this a poor specification would be pH 6.4-6.6.
This specification is poor because it does not identify the target value
Rules for Control Process
Centre the process (on the target value).
Reduce the range (the amount of variability).
What is ‘measurement error’?
This is not a measurement mistake; the personnel in charge of measurement (e.g. laboratory staff) will be highly trained
Reducing measurement error
Regular calibration, as well as by checking the equipment accuracy by measuring known standards
Why does variation occur
Variation also occurs due to sampling errors
What does a smaller sample size mean
Increased likelihood of error
What is a Run Chart
SIMPLE PROCESS CONTROL
The run chart is a graph used to study how a process changes over time. Data are plotted in time order.
Lines with LSL/USL and a Target
Goal of stats process control
The aim of statistical process control is to use simple tools to improve the process until it is well within specification.
What is Process Capability
the ability of a manufacturing process to consistently make products within a specification.
1 σ
2 σ
3 σ
1σ = 68% 2σ = 95% 3σ = 99.7%
What is a histogram?
a graphical representation that organizes a group of data points into user-specified ranges. Similar in appearance to a bar graph, the histogram condenses a data series into an easily interpreted visual by taking many data points and grouping them into logical ranges or bin (eg Bell Curve)
Standard deviation
Average amount of variation both above and below the mean results
1-3σ how much falls within 6σ
Almost all (save for outliers)
What are control charts?
They can provide early warnings as to when a process might be going out of control
reflect what is normal for a process
Why use control charts?
control chart is a graph used to study how a process changes over time.
Why use control charts?
control chart is a graph used to study how a process changes over time.
How is data plotted on Control Charts?
over time in time order
What is the difference between USL/LSL and UCL/LCL and UWL/LWL
USL/LSL - Specification Limits we set
UCL/LCL - Control Limits calc on Stan Dev from processed Info
UWL/LWL - usually 1.5 Standard Deviation for early warning
Features of Control Charts?
- Produces once process in control
- Center line is long term avg
- Control Limits (UCL/LCL) based on calculated stand devs
- Warning Limits (UWL/LWL) sometimes used 1.5 stand devs
- Rules dont let people interfere
